Water-absorbing polymer particles are used to produce diapers, tampons, sanitary napkins and other hygiene articles, but also as water-retaining agents in market gardening, agriculture or technical engineering or the like applications. The water-absorbing polymer particles are also referred to as “absorbent resins”, “superabsorbents”, “superabsorbent polymers”, “absorbent polymers”, “absorbent gelling materials”, “hydrophile polymers” or “hydrogels”.
A superabsorbing polymer in the state of an aqueous polymer gel is considered to be in a wet state; i.e. still having a considerable water content of the aqueous polymer gel before drying, in particular as outlined below. In this state preferably the aqueous polymer gel can be crosslinked; in particular, except of a residual part, practical totally crosslinked, in particular as outlined below. A superabsorbing polymer in the state of water-absorbing polymer particles is considered to be in the state of after drying; i.e. having a lower residual moisture content of the water-absorbing polymer particles after drying of the aqueous polymer gel, in particular as outlined below. In this state preferably the water-absorbing polymer particles can be postcrosslinked; in particular, except of a residual part, practical totally postcrosslinked, in particular as outlined below. The production of water-absorbing polymer particles is described in the monograph “Modern Superabsorbent Polymer Technology”, F. L. Buchholz and A. T. Graham, Wiley-VCH, 1998, pages 71 to 103. The aqueous polymer gels obtained by polymerization are typically dried by means of a forced-air belt dryer. The use of air belt dryers, in particular multistage forced air belt dryers, is proposed, wherein the material being dried is newly distributed on the next conveyer belt in each case (see also in “Perry's Chemical Engineers' Handbook”, 7th edition, McGraw-Hill, pages 12-48).
Belt dryers with conveyer belts in general are used for producing water-absorbing polymer particles like e.g. described with regard to specific relevant parameters of a conveyer belt surface roughness in US2011/0204288 A1 or a conveyer belt speed in US 2010/0041549A1 or a swivel belt in combination with a conveyer belt US 2012/0048973A1. Thus, belt dryers with conveyer belts are to be distinguished from band reactors. Wherein a band reactor is for use to produce an aqueous polymer gel from its constituents, a conveyer belt dryer is for use to produce water-absorbing polymer particles from an aqueous polymer gel, in particular to produce from a preferably practical totally crosslinked aqueous polymer gel said water-absorbing polymer particles, in particular postcrosslinked water-absorbing polymer particles.
In a contemporary conveyer belt dryer, a plate conveyer belt design of contemporary art has a pin at a joint between a first and a second belt plate and thus the connection of plates is similar to a piano hinge. A piano hinge of general type e.g. is shown in US2004/0200698A1. Here the problem arises that a gap G, as shown in FIG. 5, at the hinge line between the plates forms an openings which allow passing of particles through the openings or trapping of particles in the openings, which is unwanted. Usually material which has fallen off the belt is not or only disadvantageously recyclable and thus in general has to be considered as waste.